The present disclosure relates to a signal potential converter for converting the potential of an input signal to pass a signal having a different potential.
As the feature size of transistors has been further reduced lately, their operating voltage has become lower and lower year after year. As for external interfaces, on the other hand, their operating voltage is rated in advance in accordance with a standard. Therefore, integrated circuits need to operate at an operating voltage of 5 V or 3.3 V, for example, so as to be connectible to existing devices as well. Thus, a level shifter (signal potential converter) is used to arbitrate between a signal to be driven by a micro-transistor and a signal to be driven at, e.g., 5 V or 3.3 V. To transmit a signal at high speeds, in particular, an AC coupler using a capacitor may be used effectively.
PCT International Application Publication No. 2012/157031 discloses a configuration for reducing a variation in potential at a terminal node of a signal potential converter so as to prevent jitter from being produced in the converted signal.
According to the configuration of PCT International Application Publication No. 2012/157031, an upper limit potential and a lower limit potential are set with respect to a signal at an AC coupled terminal node such that the signal is clamped. In such a configuration, if the clamp potential difference does not agree with the amplitude of the signal, then jitter tends to be produced in the converted signal.
For example, if the amplitude of the signal is smaller than the clamp potential difference (VCLT−VCLB) as shown in FIG. 6A, then the signal level is not stabilized. On the other hand, if the amplitude of the signal is larger than the clamp potential difference (VCLT−VCLB) as shown in FIG. 6B, then the waveform of the signal will have distortion. In either case, such a phenomenon produces jitter in the converted signal.
Such a problem may be overcome by adjusting the clamp potential difference to the amplitude of the signal. However, the amplitude of the signal is affected by the supply voltage of a circuit section generating an input signal. Thus, a configuration for dynamically adjusting the clamp potential according to the supply voltage on an input end is required.
Thus, the present disclosure provides a signal potential converter configured to adjust dynamically a clamp potential according to a supply voltage on an input end.